1. Field of the Invention
This invention relates to fluid flow detection switches and flow meters and more particularly, relates to flow switches and flow meters that incorporate shaped flexible targets that are deflected by the fluid flow via a flow sensitive bending beam and, are very sensitive; include electronic signal processing interfacing to provide flow switch flow meter and flow totalizer output information via a Hall Effect transducer.
2. Background Information
This invention is an improvement to existing flow switches and meters, such as that disclosed and claimed in U.S. Pat. No. 5,021,619 issued to the same inventor as the device disclosed and described herein, incorporated herein by reference.
The patent referred to above disclose a cantilevered flat flow sensing spring blade disposed to extend into the flow of a fluid through a pipe or conduit. The fluid flow drag forces bends the spring until the spring comes to rest against a hollow support tube located downstream of the spring. The support tube holds the spring steady to protect it from excessive stress and vibration induced by turbulent fluid flow.
In the prior art, devices known as "bending beam fluid flow switches and meters," the flow sensing spring activates a reed switch inside the support tube from the effect of a magnet moving closer to the support tube. This provides an indication of a certain level of flow rate.
The switch triggering fluid flow rate is determined by adjusting the size, shape and stiffness of the spring supporting the magnet. Such magnet operated reed switches have an inherent hysteresis in their operation as the magnet approaches and recedes from the reed switch. At some point, the magnet is attracted to the reed switch by a magnetic force and quickly moves the last bit of distance to the support flow tube under the influence of the magnetic effect rather than because of the fluid force on the flow target spring thus, introducing potential errors into flow measurement.
The reed switch itself also has another mechanical hysteresis effect. This effect is that once closed, the switch tends to latch in the closed position; again by nonlinear magnetic attraction. Thus, when fluid flow declines, the reed switch still stays closed momentarily until the magnetic force between the magnet and the reed switch internal members no longer are able to resist their tendency to return to their normal relaxed position. Therefore, at this instant, the two magnetic members of the reed switch decouple and snap back to their normal relaxed positions and the switch opens. However, the fluid flow rate when the switch opens, will be below the fluid flow reed rate at which the switch closes. This is the magnetic/mechanical hysteresis interaction between the magnet and reed switch producing the related flow differential between the on and off condition, and is known as the "on-off hysteresis." In some situations, the hysteresis is a useful phenomenon because it prevents the switch from chattering on and off due to flow turbulence when the flow rate happens to be right at the switch triggering point.
In effect, the double magnetic latch, unlatch hysteresis of the magnet and reed switch internal blades create a fluid flow hysteresis dead band which reduces flow measuring sensitivity near the flow switch point. The magnetic hysteresis system and thus, the flow turbulence hysteresis system is completely determined by local magnetic fields of the magnetic/reed switch combination, which is a phenomenon attributed to each particular magnetic/reed switch combination and cannot be adjusted except by changing one or both members.
It is therefore, one object of the present invention to employ Hall effect transducer technology to provide no mechanical magnetic coupling hysteresis since the Hall effect transducer body and internal components are non-magnetic and thus, totally magnetically transparent.
Yet another object of the present invention is to provide a Hall effect flow switch and analog flow meter that employs a very small repeatable and adjustable electronic hysteresis to ensure downstream electronic systems do not go into electronic oscillation.
It is another object of the present invention to provide a flow switch and flow meter that provides a flow induced variable magnetic field applied to a Hall effect transducer, which in turn provides a variable electronic output signal that precisely represents the fluid flow field through a pipe or equivalent conduit.
Yet another object of the present invention is to provide a flow switch and meter that employs Hall effect magnetically sensitive transducers in a digital mode and flow in a continuous analog output mode.
Yet another object of the present invention is to provide a fluid flow switch and flow meter that employs a Hall effect transducer with a variable magnetic field intensity obtained from a variety of magnet shapes, materials and strengths.
Yet another object of the present invention is to provide a fluid flow switch and flow meter for measuring the flow of fluids, gases and vapors impinging upon a flow sensitive bending arm, and employing a Hall effect transducer to produce a variable output voltage which is then translated by electronic processing circuitry into flow output information.
Yet another object of the present invention is to provide a flow switch and flow meter employing a Hall effect transducer, employing a variety of magnetic shapes, materials and configurations that include a direct in-line application of a magnet moving toward a Hall effect device or a sideways offset magnet moving past a Hall effect device.
Still another object of the present invention is to provide a flow switch and flow meter that has improved sensitivity by measuring the output of the Hall Effect transducer caused by fluid flow vortex shedding, at and down stream of flow sensitive bending beam.
Yet another object of the present invention is to provide a flow switch and flow meter that includes appendages on a bending beam to enhance the vortex shedding to further improve sensitivity.